A large amount of polyurethane resins have been used in a variety of fields such as resins for coatings, adhesives, dispersants for inks, ultraviolet ray curable or electronic beam curable resins, and foams, etc.
Of the urethane resins, as a urethane resin having lactone chains in the main structure has excellent properties as polyurethanes, it has been widely employed.
In the case when the urethane resin having lactone chains is modified as a hydrophilic urethane resin for the purpose of preparing water-based inks or coatings, it has been carried out that amino groups are introduced into the urethane resin.
Also, in the case of intending to improve an anti-strippability of coatings or adhesives from a substrate, and in the case of intending to improve dispersity of inorganic fillers such as magnetic powders in a urethane resin as a binder for magnetic tapes, there has been carried out the introduction of amino groups into the urethane resin.
For example, Japanese Patent Kokai No. 62-218456 discloses that a polycaprolactone having amino groups and urethane resins therefrom can be prepared by the addition reaction of lactone monomers to diamines such as methyliminobisethylene diamine, etc. or to an aminoalcohol such as N-methyldiethanol amine.
It has been conventionally known that lactone monomers can be introduced into hydroxyl group and amino groups by ring-opening addition polymerization, and lactones having amino groups have been prepared by the addition polymerization of lactone monomers to amino alcohol, etc., by heating at 100 to 200.degree. C. in the presence of catalysts.
However, in the case when amines are allowed to thermally react at the above-mentioned reaction conditions, there colors a polycaprolactone having amino groups which is a resulting polymer in a succeeding step, inevitably resulting in that a urethane resin prepared therefrom also colors.
Although it can be prevented to color in preparing the polycaprolactone by the reaction at a temperature below 100.degree. C., reaction period is considerably lengthened, unpreferably resulting in becoming problematic from a viewpoint of commercial production.
The coloration is a serious problem in the case when the polyurethane resin is employed as resins for coatings, inks, ultraviolet ray curable or electronic beam curable resins, etc., and even though excellent properties are obtained in the urethane resins, the colored polylactone having amino groups cannot be substantially employed.
Furthermore, as the polylactone having amino groups derived from a diamine has amide groups, a cohesive force becomes strong. As the result, in the case when lactone chains are short, it unpreferably results in becoming poor in solubility in solvents and compatibility with other resins.
In the meantime, a variety of dispersants have been employed for the purpose of improving dispersity of pigments and storage stability of coatings, reducing a period for dispersing, preventing separation of pigments or dyes, and improving gloss of coated layer or printed surface in the use of coating compositions and inks. Generally speaking, the dispersants to be employed for such the purposes contain functional groups capable of adsorbing pigments and polymer chains composed of polyester or acrylic units having a good compatibility with vehicles for coatings or inks.
There are disclosed a variety of dispersants having amino groups as the functional groups capable of adsorbing pigments.
For example, Japanese Patent Kokai No. 103988/1978 discloses amino compounds having a low molecular weight such as N,N-dimethylaminopropylamine, and Japanese Patent Kokai No. 174939/1986 discloses dispersants for pigments comprising a polyethylene imine which is an amine compound having a high molecular weight. These dispersants for pigments have molecular structures in which polyester chains are combined with polyamines through amide bonds. However, compounds having amide bonds are very strong in cohesive force, as the result, there are problems that the compounds are low in solubility into many solvents for coatings.
Furthermore, nitrogens in the amide bonds do not exhibit adsorption onto pigments because nitrogens in the amide bonds are exceedingly weak in basicity.
For the purpose of improving stability in dispersity by effectively forming a sterically repulsive layer on the surface of pigments, there can be possibly thought an attempt that many amounts of polyester chains are grafted to polyamine chains.
However, grafting of polyester chains results in decreasing the amount of functional groups for adsorbing, unpreferably resulting in causing a problem of decreasing dispersity.
Furthermore, a reaction for grafting polyester chains to polyamine chains requires a temperature ranging from 100 to 150.degree. C. at the lowest in order to attain an appropriate reaction rate.
When starting materials containing amines are heated at the reaction temperature, coloring of a reaction product is almost unavoidable. Accordingly, in light colored coatings, particularly in white colored coatings, it results in becoming problematic.
In view of such the situations, and as a result of extensive investigations, the present inventor has now completed the present invention.